1. Field of the Invention The present invention is in the field of heating air by exothermic catalytic oxidation of a small fraction of hydrogen gas mixed with the air.
2. Description of the Prior Art
There is a widespread need for apparatus capable of producing heated air for several end uses, and in most cases such need is for air heating apparatus which is self-contained, compact, and lightweight so as to be conveniently portable The most important current need for such air heating apparatus is to produce heated air to be inspired by persons through a face mask or other suitable device into the lungs, which is an efficient means for warming persons suffering from body core heat loss that may have reached the stage of hypothermia, i.e., the body core temperature may have become reduced down to 94.0.degree. F. or lower from the normal body core temperature of 98.6.degree. F. Such inspiration of heated air directly into the lungs is the quickest possible way to warm a person, and it is in no way harmful, as some systems for warming a person can be; in fact, breathing heated air can be beneficial.
Much of this need for heated air is to combat hypothermia in medical emergency situations, but there is also widespread need in connection with hypothermia that is either unavoidable or deliberately induced during surgery. The medical needs for heated air to combat hypothermia are the most important present needs.
The medical emergency hypothermia problems fall into two separate categories, the "accidental hypothermia" problems and the "urban hypothermia" problems. Examples of typical accidental hypothermia situations are a car crashing into a very cold river, an accidental near-drowning, a child lost overnight, a skiing accident, or a small boat accident in which the boat sinks or burns and its occupants must jump into very cold water. Examples of urban hypothermia are alcohol or other drug-induced cold, stroke victims, or the tendency which some older people have to run lower than normal body temperatures because of slower heart rates and blood circulation, and poor body conductivity.
There are several hypothermia problems involved in surgery. In general, every time someone undergoes surgery they are placed in an environment where they have a minimal amount of clothing, especially if they are having major surgery where there is no clothing involved and there are just a few surgical drapes. All surgical patients are affected by hypothermia, the degree of which is determined at least in part by the length of the surgical procedure. Hypothermia is the greatest problem for anesthesiologists. Hypothermia otherwise caused during surgery complicates the anesthetic application problems. Also, the anesthetic gases and some other anesthetic agents will produce slower blood flows and other metabolic changes which will induce hypothermia. It is recognized that eight of the thirteen commonly used anesthetics produce hypothermia. Additionally, during organ transplant and heart surgical procedures the patient is routinely cooled to a temperature far below the 94.0.degree. F. hypothermia level, commonly to approximately 77.degree. F., and in some instances to as low as 68.degree. F. To indicate the extent of this problem, there are approximately 240,000 heart procedures performed each year.
The important thing in such surgical hypothermia is to be able to control the body core temperature of the patient. Regardless of whether the hypothermia is deliberately or inadvertently induced during surgery, it is important to be able to rewarm the patient quickly and safely. The problem now is that the rewarming techniques employed in recovery after surgery are slow, and some of them can cause damage. One rewarming technique is the use of heating blankets, but this is very slow. Another common technique is to use a blood warming device on the profusion pump, which in layman's terms is the heart/lung machine. However, if the heart/lung machine is depended upon to rewarm the body, the longer it is necessary to circulate the blood through the machine, the more hemolysis that is caused (hemolysis being the breaking apart of red blood cells). Thus, most currently used rewarming techniques after surgery are external to the body.
However, it has been determined that rewarming the patient internally by having the patient breathe warm air is a more effective way of heating the body from a hypothermic condition. The most current apparatus that is used in medicine for this purpose is made by Bennett-Cascade, this apparatus having an electrically powered heat source over which water is cascaded every time the patient breathes in. However, this has the problems that there is very little temperature control, and a temperature gradient of at least about 10.degree. F. in the delivery tubing tends to cause a considerable amount of water condensation in the tubing which, if it enters the lungs, can restrict the amount of gas exchange in the lungs. Additionally, as a patient starts to awaken, he will tend to fight off the heavy humidity and extra water.
Another serious hypothermia problem is one that can accidentally occur during deep sea diving, particularly commercial diving. Divers will routinely work in the range of from about 700-1300 foot depths out of a diving bell or platform, and during these operations they are warmed by hot water suits. Under normal conditions without the hot water suits, all of the metabolic production of heat at such depths where the temperature is 39.4.degree. F. is lost through the respiration regardless of what is done to protect the body. Even with the hot water suits the divers are losing heat, but once the hot water suits are cut off from their source of hot water, as in an emergency, suddenly the divers are in a grave situation. The diving bell or platform will normally have from seven to nine cylinders of a compressed helium/oxygen gas so that there would be enough of such artificial air mix to last approximately three days. However, the divers would freeze to death, even in survival suits, within eight hours. Thus, there is an important need for warm air breathing apparatus to cope with hypothermia in diving situations. By inspiring warm air directly into the body via the lungs, the heat losses from the severe cold and high thermal outlet conductivity of the salt water can be completely overcome.
There are a number of institutions and geographical regions where it would be highly desirable to have apparatus for providing warm breathing air that is self-contained, compact, light in weight and readily portable. Examples of these are the military for coping with a variety of military-type accidents; the Coast Guard for small vessel rescue work; ski resorts because of the frequency of ski accidents and the severe cold environment; mountain communities; and expeditions to colder climates such as Antarctica, and Nepal and Switzerland where a great deal of mountain climbing occurs. In remote locations such as these people are often days away from any help, so that they would usually die without the prompt thermal help against hypothermia that would be available with warm air breathing apparatus.
While it will be seen from the foregoing that the principal uses currently envisioned for a catalytic air heating system are for warming air or other breathing gas to combat hypothermia, there are other currently envisioned uses for a catalytic air heating system. One of these is for warming the intake air of an internal combustion engine to improve fuel vaporization in a cold climate situation. Another is the warming of an electric storage battery by enshrouding it in heated air. Another is for warming a space, such as a room or rooms of a building.
Applicant is aware of the Castel U.S. Pat. No. 4,016,878 which teaches the heating of breathing air by the exothermic oxidation of a small percentage of hydrogen gas mixed with the air. The Castel patent teaches storing the air/hydrogen mixture in a pressure cylinder and releasing it through a catalyst bed in a simple straight-through flow to a breathing mouthpiece or mask. While the Castel system does indeed heat the breathing air, it is much too slow in building up sufficient heat to reach a target temperature, and large temperature fluctuations occur between inspiration and expiration. For these reasons, the Castel apparatus has not found commercial acceptance for combating hypothermia in the many situations where air warming apparatus could be useful as indicated above.